May 23, 2013

Small, Plant-Eating Dino Sheds Light On Ancient Ecosystem

Although most of us imagine dinosaurs as large, fierce animals, a team of paleontologists from the University of Toronto, Royal Ontario Museum, Cleveland Museum of Natural History and University of Calgary“¯have highlighted a previously overlooked diversity of small dinosaurs. The study, published in the Journal of Vertebrate Paleontology, describes a new dinosaur — the smallest plant-eating dinosaur species known from Canada — the Albertadromeussyntarsus.

The relatively tiny dinosaur, which was only about five feet long and weighed approximately 30 pounds, was identified from a partial hind leg and other skeletal fragments. Roughly the size of a large modern turkey, the remains of the Albertadromeus reveal that it was a speedy runner.

Albertadromeus lived about 77 million years ago during the Late Cretaceous, in what is now southern Alberta. The dinosaur´s name, Albertadromeus syntarsus, means “Alberta runner with fused foot bones.” The two fused lower leg bones would have made this dinosaur a agile two-legged runner, unlike its larger ornithopod cousins, the duckbilled dinosaurs. Albertadromeus is the smallest known plant-eating dinosaur in its ecosystem. The research team hypothesize that it used its speed to avoid predation by the many species of meat-eating dinosaurs that lived during the same period.

David Evans of the Royal Ontario Museum discovered Albertadromeus in 2009 as part of an on-going collaboration with Michael Ryan of the Cleveland Museum of Natural History. The two have been investigating the evolution of dinosaurs in the Late Cretaceous of North America, which was dominated by large-bodied plant-eating dinosaurs.

The scientists say that so few small-bodied dinosaurs are known in North America because smaller animals are less likely to be preserved. Their bones are more delicate and are often destroyed before being fossilized.

"We know from our previous research that there are preservational biases against the bones of these small dinosaurs," explained Caleb Brown of the University of Toronto. "We are now starting to uncover this hidden diversity, and although skeletons of these small ornithopods are both rare and fragmentary, our study shows that these dinosaurs were more abundant in their ecosystems than previously thought."

A combination of the taphonomic processes (those related to decay and preservation) described above and biases in the way that material has been collected have previously limited paleontologists´ understanding of these smaller dinosaurs. Carnivores, scavengers and weathering processes are more prone to destroying the bones of smaller animals, leaving fewer smaller animals to become fossils. Smaller animal fossils are often more difficult to find and identify than those of larger animals.

"Albertadromeus may have been close to the bottom of the dinosaur food chain but without dinosaurs like it you'd not have giants like“¯T. rex," said Michael Ryan. "Our understanding of the structure of dinosaur ecosystems is dependent on the fossils that have been preserved. Fragmentary, but important, specimens like that of“¯Albertadromeus suggest that we are only beginning to understand the shape of dinosaur diversity and the structure of their communities."

"You can imagine such small dinosaurs filling the niche of animals such as rabbits and being major, but relatively inconspicuous, members of their ecological community," added Anthony Russell of the University of Calgary.